The invention relates to a valve rotator according to the preamble of claim 1.
In internal combustion engines, particularly large diesel engines, the valve seat and valve stem are subject to strong wear. In order to bring about a uniform thermal loading and abrasion, use is normally made of a valve rotator. Rotation additionally ensures the decarbonization of the valve seat.
A valve rotator according to the preamble is known from U.S. Pat. No. 2,624,323. In the latter case a disk spring is spaced from balls, which produce the rotary movement. In order to reduce the frictional forces between the axial spring device and a cover, there is a three-point support with inserted balls on one disk spring side.
In other conventional valve rotators, such as those of DE-AS 1 293 789, U.S. Pat. No. 2,827,886, DE-OS 27 57 455 or 30 04 320, the cover, which is simultaneously the lower valve spring disk, is mounted in rotary manner by means of a disk spring, which rests directly on the balls of the body. When the valve is closed the balls are held by the tangential springs at the upper point of the inclined ball race. If the valve is opened, the disk spring presses on the balls and the latter roll to the lowest point of the inclined ball race in the body. They rotate the disk spring and press together the tangential springs. The rotary movement of the disk spring is transferred via the cover, the valve spring, the upper spring disk and the shims to the valve. If the valve is closed, the disk spring is relieved. The balls are moved back into the starting position again by the tangential springs without rolling.
Although this known valve rotator leads to a good rotation, its service life is limited, since the force introduction of the valve spring force takes place in the case of the known valve rotator via the disk spring and the balls in the body. Thus, both on the balls and on the ball races in the ball pockets considerable wear occurs and this is referred to as pitting. As a result of the function there is also a pronounced deformation, bending and squeezing of the disk spring, particularly if a so-called overpressing occurs when the valve setting is not precise.
The object of the invention is to provide a valve rotator having a simple construction and a good rotation function, whilst at the same time being subject to limited wear.
The invention achieves this object through a valve rotator having the features of claim 1. Preferred further developments of the invention appear in the dependent claims.
A fundamental idea of the invention is to separate from one another in a logical manner the rotation principle and the necessary force introduction and transfer principle. If the valve rotator is compressed, accompanied by the introduction of a valve spring force or tension, the axial spring takes up the essential forces. As a result of the force transfer means constituted by the pivot bearing/axial spring device/cover, the upper part of the valve rotator is frictionally interconnected under the valve spring tension. During a vertical movement, reducing the spacing between the cover and the body, the outer face of the cover rotates the body via the antifriction or roller bearing. This rotation takes place relative to the cover via frictional engagement between the components coverxe2x80x94ballsxe2x80x94body. In the case of a load removal these components are separated from one another, accompanied by an increase in the vertical spacing and as a result of the tension of the tangential springs the balls again assume their starting position. Thus, a further rotation of the body can be initiated during the next stroke. The antifriction bearing reduces friction and wear. Through the external arrangement of the balls, their circumferential rolling forces as a result of the relatively large spacing from the rotation axis brings about a high torque, which improves rotation.
It is essential that the spring action and rotation of the rotator are decoupled. As the axial spring device is arranged separately and in spaced manner with respect to the balls, the latter and the ball races are scarcely axially loaded. In this way there is an extensive elimination of pitting formation on the balls and in the ball pockets and consequently wear on the valve rotator. The axial spring device is also no longer exposed to bending, deformation and squeezing forces, which in the case of the known valve rotator occur on the known disk spring. The associated wear phenomena on the disk spring are consequently largely avoided with the valve rotator according to the invention. Compared with the known valve rotator, the valve rotator according to the invention drastically improves the service life, which constitutes an enormous economic advantage, particularly with long-life internal combustion engines. The antifriction bearing has as standard components two bearing track rings between which the rolling elements are located in a cage.
According to the invention the cover is mounted and guided about the rotation axis relative to the body by the antifriction bearing. In the case of an axial displacement of the cover relative to the body, the rotary movement produced is exclusively radially guided by the needle bearing. There is no contact between the cover and the body. For said radial guidance the axial needle bearing has conically positioned bearing track rings or lateral edge shoulders on the two bearing track rings, between which are located the cylindrical, needle-like rolling elements with their cage.
Preferably, according to a further development of the invention, there are three to six and preferably four ball pockets, which are uniformly distributed along the circumference of the body. Compared with conventional valve rotators, according to the invention a much smaller number of balls can be provided, because the individual balls are scarcely loaded or stressed. For a constant number of balls, roughly eight to ten, the ball diameter can be roughly halved, so that it is between 3 and 10 mm. This considerably reduces costs during the manufacture of the body and the ball races therein.
Whereas in the case of the known valve rotator the inclination of the ball races is relatively small, according to the invention it is preferable for the inclination of the ball race of the ball pockets to be uniform and namely between 6 and 15xc2x0. As a result of the limited loading of the individual balls in the case of the valve rotator according to the invention, the pre-requisite for a greater ball race inclination is created, so that the rotary movement is improved.
According to a preferred embodiment of the invention, the axial spring device comprises at least one disk spring, preferably a disk spring unit. Disk springs represent a particularly cost-effective possibility of pressing axially apart the cover and the body. When using a disk spring unit the desired axial forces can be inexpensively obtained with high precision.
The pivot bearing located on one axial side of the axial spring device, can be located either on the cover or on the body, the latter being preferred. The pivot bearing can be a simple slideway. However, according to the invention, it is preferable for the pivot bearing to be a needle bearing. In the case of this antifriction bearing variant, in a small construction space there is a particularly low friction rotation between the disk spring supported frictionally on the body on the one hand and the cover on the other.
An overpressing of the valve rotator is inventively prevented in that the balls are completely received in the ball pocket on the lower point of the ball race and that the body in this position engages against the cover. On reaching the maximum axial displacement path, the cover comes up against a block, so that the flux of force is directly passed by the cover into the body. An overstressing of the balls or the axial spring device is consequently prevented, which also has a positive effect on the service life of the valve rotator.
The body is firmly connected to the cylinder head, the cover serving as the lower valve spring disk and is connected in non-rotary manner thereto. However, it is also possible to have a reverse arrangement of the valve rotator according to the invention or a so-called upper arrangement in which the cover forms the upper valve spring disk.